The present invention relates to a production method of a formed article made from a high performance polymer, particularly a polymer superior in mechanical strength and heat resistance.
Polymers having rigid units, such as a para bond of aromatic ring and the like, in the main chain have high heat resistance and are superior in dynamic properties. Of such polymers, polybenzazole has extremely high heat resistance. It is known that these polymers are polymerized and formed into articles in the presence of polyphosphoric acid as a solvent (Wolfe et al., Macromolecules, 1981, pp. 909 and 915). These polymers obtained by using such a polyphosphoric acid solvent have been evaluated as to the performance at a laboratory level, but have not been produced industrially until recently. Therefore, problems associated with the industrial practice of these polymers have not drawn much attention.
In a reactor where a shear force is applied during polymerization and processing of these high performance polymers into a fiber, film and the like, in a pump that delivers a polymer solution, and in a pump that discharges a given amount of the polymer solution from a spinneret, the temperature is often raised beyond 160xc2x0 C. during the step to reduce the viscosity coefficient of the polymer solution to a level sufficient to facilitate the processing. In addition, the temperature may become still higher due to the heat generated by the shear force applied in the apparatus. In this event, conventional corrosion-resistant materials, such as SUS 316 L and Stellite (MITSUBISHI MATERIALS CORPORATION), are defective in that a part of an apparatus elutes out due to the corrosion of a metal by the action of polyphosphoric acid, which in turn makes the solvent nonrecyclable, and the service life of the apparatus is shortened.
It is therefore an object of the present invention to improve a material of conventional apparatuses used for polymerizing and processing high performance polymers in a polyphosphoric acid solvent, thereby to elongate the service life of reactors and pumps and to reduce the metal ion concentration of the solvent to be recycled.
That is, the present invention provides a method for producing a formed article from a dope comprising a polyphosphoric acid solvent and a polymer soluble in polyphosphoric acid, which comprises using a production apparatus comprising an apparatus for stirring and uniformly dispersing or homogenizing a dope and a pump apparatus for delivering the uniformly dispersed or homogeneous dope, wherein at least one of the apparatus and the pump apparatus has a part that comes into contact with the dope, which part is made of a corrosion-resistant material having a material elution rate of not more than 1 (mm/year) in a 116% polyphosphoric acid at 210xc2x0 C.
Preferably, the present invention provides a method for producing a formed article from a polyphosphoric acid solution, wherein a corrosion-resistant material has a hardness of not less than HRC 20.
The present invention also provides a method for producing a formed article from a dope comprising a polyphosphoric acid solvent and a polymer soluble in polyphosphoric acid, which comprises using a filter made of a corrosion-resistant material having a material elution rate of not more than 0.1 (mm/year) in 116% polyphosphoric acid at a filtering temperature, before discharge of the dope from a spinneret.